The amygdala is known to play a critical role in emotional responses particularly fear, in both humans and animals. The amygdala and its afferent and efferent connections comprise a major component of the auditory fear conditioning circuitry. The long-term objective of this research is to characterize pre- and postsynaptic modifications in amygdala glutamatergic neurotransmission underlying the expression of learned fear. Preliminary data show significant alterations in synaptic transmission in the internal capsule (IC) fiber pathway from the medial geniculate to the dorsal lateral amygdala recorded in vitro in amygdala slices from paired fear conditioned but not unpaired control animals. The proposed experiments using the fear-potentiated startle paradigm will test the hypothesis that lasting potentiation of synaptic transmission occurs at particular synapses within the fear conditioning intraamygdala circuitry. The following specific aims will be addressed using whole cell patch recording in amygdala slice preparations from three populations of animals. naive control, unpaired control and paired fear conditioned animals: 1) Characterize the modifications in synaptic transmission and membrane conductance underlying fear conditioning and determine the pre- and post-synaptic changes in N-methyl-D-aspartate (NMDA)- and non-NMDA-mediated synaptic transmission in animals exposed to a paired conditioned stimulus (CS) and aversive stimulus (UCS) with those exposed to the same information but in an unpaired paradigm and 2) trace the information flow through the amygdala by comparing in the three populations of animals the synaptic modifications occurring in glutamatergic transmission at different synapses in the amygdala fear conditioning circuitry. The results of the proposed experiments will enhance our understanding of the membrane mechanisms underlying emotional learning at the membrane and whole cell level and provide important information about changes in the essential elements of interneuronal communication within a key structure involved in emotion, the amygdala. Ultimately the proposed studies may provide insight into potential therapeutic strategies in the treatment of neuropsychiatric disorders such as anxiety, phobia, schizophrenia and in particular posttraumatic stress disorder.